CONTENTS
CONTENTS
|
PAGE
|
Abstract
|
2
|
Introduction
|
3
|
Literature review
|
5
|
Objectives
|
7
|
Methodology
|
8
|
Results
|
10
|
Discussion
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16
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Conclusion and recommendation
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19
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Reference
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20
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Appendix
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21
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Abstract
This experiment is
about calorimeter. This experiment was divided into two parts, Part A and Part
B. Part A was carried out to determine
the specific heat of metal, where copper was used in this experiment.Part B was
carried out to determine the quantity and direction of heat flow for the
dissolution of a salt, which was natriumthiosulphate, Na2S3O2.
For part A and B,
polyform cups filled with water were used as the calorimeters. Thermometer was
used to measure the change of temperature when the substances were added into
each calorimeter. For Part A, copper was heated in a water bath, and then
transferred into the calorimeter. The temperature of the water bath, the
initial temperature and temperature change in calorimeter were measured with a
thermometer. The weights of water and copper were also measured with an
electronic balance. This information obtained from the experiment was used to
calculate the specific heat of copper.
For Part B, the salt Na2S2O3is
added into water where it dissoluted. Similar to Part A, the information and
result were recorded to calculate for the quantity of heat transferred, and the
direction of transfer.
During the experiment,
several errors occurred. As too much time was taken to transfer the substances
into the calorimeter, there was heat transfer between the surrounding and the
substances. Na2S2O3 salt did not dissolve
completely after swirling, causing the reaction to be incomplete. Besides, the
heat from the apparatus might be absorbed into the water and substances. Heat
was also produced during the stirring process. There were some errors when the
readings of the temperature and the weight of calorimeter, water, copper and Na2S2O3were
taken.
A calorimeter from Latin,
meaning heat
and it is a device used for calorimetry, the science of
measuring the heat of chemical reactions or physical changes as
well as heat capacity.A simple calorimeter just
consists of a thermometer attached to a metal container full of water suspended
above a combustion chamber.Differential scanning calorimeters, isothermal micro
calorimeters, titration calorimeters and accelerated rate calorimeters are
among the most common types.
The
world’s first ice-calorimeter,
used in the winter of 1782-83, by Antoine Lavoisier and Pierre-Simon
Laplace, to determine the heat
evolved in various chemical changes;
calculations which were based on Joseph Black’s prior discovery of latent heat. These experiments mark
the foundation of thermo
chemistry. I this experiment, we use
Styrofoam cup. It is a coffee cup
calorimeter -
usually filled with water, include a lid on the cup with an inserted
thermometer.in
fact, the quantity of energy gained or lost is given by the equation:
Q = mwater•Cwater•ΔTwater
Where Cwater is
4.18 J/g/°C.
The mass of
water and the temperature change of the water in the coffee cup calorimeter can
be measured; the quantity of energy gained or lost by the water can be
calculated.if an attempt is being made to determine the specific heat of fusion
of ice using a coffee cup calorimeter, then the assumption is that the energy
gained by the ice when melting is equal to the energy lost by the surrounding
water.It is assumed that there is a heat exchange between the ice and
the water in the cup and that no other objects are involved in the heat
exchanged and the equation could be given as below:
Qice =
- Qsurroundings =
-Qcalorimeter
The heat exchanged in a calorimeter should be between the
water and the system; heat should not be lost to the surrounding air.The
change in temperature is determined by measuring the initial temperature, T1,
of the reactants, and the maximum temperature, T2, of the contents
of the calorimeter during the exothermic reaction
Heat capacity (C) is the amount of heat (q) required to raise the temperature of
an object one degree Celsius.
The units for heat capacity are J/oC.
(The unit is read as Joules per degree
Celsius).
The equation which describes this
relationship is:
C = q/DT
C =
is the heat capacity of the object
q = is the amount of heat entering or
leaving the object
The change in temperature
(DT) of the object is defined
as: DT = Tfinal - Tinitial
A
positive value for heat (+q) means that heat is absorb into the system. And a
negative value for heat (-q ) means that heat is release from the system.
Literature view
Calorimetry, derived from the Latin calor meaning heat, and
the Greek metry meaning to measure, is the science of measuring the amount of
heat. All calorimetric techniques are therefore based on the measurement of
heat that may be generated (exothermic process), consumed (endothermic process)
or simply dissipated by a sample. There are numerous methods to measure such
heat, and since calorimetry's advent in the late 18th century, a large number
of techniques have been developed. Initially techniques were based on simple
thermometric (temperature measurement) methods, but more recently, advances in
electronics and control have added a new dimension to calorimetry, enabling
users to collect data and maintain samples under conditions that were
previously not possible.
Example of
specific heat depend on temperature
To illustrate the role of various degrees of
freedom in storing heat, we may consider nitrogen, a diatomic molecule that has five active degrees of
freedom at room temperature: the three comprising translational motion plus two
rotational degrees of freedom internally. Although the constant-volume molar
heat capacity of nitrogen at this temperature is five-thirds that of monatomic
gases, on a per-mole of atoms basis, it is five-sixths that of a monatomic gas.
The reason for this is the loss of a degree of freedom due to the bond when it
does not allow storage of thermal energy. Two separate nitrogen atoms would
have a total of six degrees of freedom—the three translational degrees of
freedom of each atom. When the atoms are bonded the molecule will still only
have three translational degrees of freedom, as the two atoms in the molecule
move as one. However, the molecule cannot be treated as a point object, and the
moment of inertia has increased sufficiently about two axes to allow two
rotational degrees of freedom to be active at room temperature to give five
degrees of freedom. The moment of inertia about the third axis remains small,
as this is the axis passing through the centres of the two atoms, and so is
similar to the small moment of inertia for atoms of a monatomic gas. Thus, this
degree of freedom does not act to store heat, and does not contribute to the
heat capacity of nitrogen. The heat capacity per atom for
nitrogen is therefore less than for a monatomic gas, so long as the temperature
remains low enough that no vibrational degrees of freedom are activated.
At higher temperatures, however, nitrogen gas
gains two more degrees of internal freedom, as the molecule is excited into
higher vibrational modes which store thermal energy. Now the bond is
contributing heat capacity, and is contributing more than if the atoms were not
bonded. With full thermal excitation of bond vibration, the heat capacity per
volume or mole of molecules approaches seven-thirds that of monatomic gases, or
seven-sixths of monatomic, on a mole-of-atoms basis. This is now a higher heat
capacity per atom than the monatomic figure, because the vibrational mode
enables an extra degree of potential energy freedom per pair
of atoms, which monatomic gases cannot possess. See thermodynamic
temperaturefor
more information on translational motions, kinetic (heat) energy, and their
relationship to temperature.
However, even at these large temperatures
where gaseous nitrogen stores 7/6 ths of the energy per
atom of a monatomic gas (making it more efficient at storing energy on
an atomic basis), it still only stores 7/12 ths of the
maximal per-atom heat capacity of a solid, meaning it is not as efficient on an
atomic basis, as substances can be. This is because many of the potential bonds
which might be storing potential energy in gaseous nitrogen (as opposed to
solid nitrogen) are lacking, because only one of the spacial dimensions for
each nitrogen atom offers a bond into which potential energy can be stored,
without increasing the kinetic energy of the atom. In general, solids are most
efficient, on an atomic basis, at storing thermal energy (that is, they have
the highest per-atom or per-mole-of-atoms heat capacity).
The specific heat (s) of a
substance is the amount of heat required to raise the temperature of one gram
of the substance by one degree Celsius. The heat capacity (C) of a substance is
the amount of heat required to raise the given quantity of the substance by one
degree Celsius. Specific heat is an intensive property, whereas heat capacity
is an extensive property. The relationship between the heat capacity and
specific heat of a substance is
C = ms
where m is the mass of the substance in grams.
ands is specific heat capacity of substance.
If we know the specific heat and
the amount of a substance, then the change in the sample’s temperature (∆t)
will tell us the amount of heat (q) that has been absorbed or released in a
particular process. The equation for calculating the heat change is given by
q = ms∆t or q = C∆t
where m is the mass of the sample in grams and
∆t is the temperature
change.
∆t = tfinal–
tinitial
The sign convention for q is the same as for enthalpy change;
q is positive for endothermic processes and negative for exothermic processes.
Objectives
·
To
determine the specific heat of a metal.
In this experiment, copper was
chosen as the metal, where its specific heat was determined from calculation.
The results of the experiment provided the information required to calculate
the specific heat.
·
To
determine the quantity and direction of heat flow for the dissolution of a salt.
Natriumtiosulphate, Na2S2O3
was used in this experiment. Quantity of heat flow, which is heat
capacity, was calculated. The rise or drop in temperature determined the
direction of heat flow.
Methodology
Materials
Calorimeter, thermometer, beaker 400 ml, test tube, Bunsen
burner, wire gauze, graduated cylinder, three finger clamp, copper,
natriumtiosulphate
Methods
A. Specific Heat of a Metal.
1. 2g
of copper is weighed and transferred into a dry test tube. The test tube is
placed in a 400ml beaker. Then, the beaker is filled with water until it is
well above the level of the metal sample in the test tube. The water is boiled
using a heater and this temperature is maintained for at least 5 minutes so
that the metal reaches thermal equilibrium with water. The temperature is
recorded.
2. The
mass of the calorimeter is weighed. By using a graduated cylinder, 20.0ml of
water is added into the calorimeter. The combined mass of the calorimeter and
water is determined. The thermometer is secured with a clamp and positioned
below the water surface. The system is allowed 5 minutes to reach thermal
equilibrium; then the temperature is recorded over 60 second intervals.
3. The
test tube is removed from the boiling water and only the copper is quickly
transferred into the calorimeter. The lid is replaced and the content is
stirred gently. The water temperature is recorded as a function of time (about
30 second intervals) for 3 minutes.
4. The
temperature (y axis) versus time (x axis) graph is plotted. ∆T is determined
from the curve and then the calculations indicated on the report sheet are
done.
B. Enthalpy (Heat) of Solution for the
Dissolution of a Salt
1. The
mass of the dry calorimeter is weighed. Using graduated cylinder, 20.0ml of
distilled water is added into the calorimeter and its temperature is recorded.
The temperature is recorded for 60 seconds with 15 seconds interval. The
combined mass of the calorimeter and water is reweighed. After that, the
thermometer is positioned below the water surface.
2. 5.0g
of the natriumthiosulphate, Na2S2O3 salt is
weighed.
3. The
salt is added to the calorimeter; the lid is replaced and gently stirred until
the salt dissolves. The temperature and time is read and recorded at 15 seconds
intervals for 3 minutes.
4.
A temperature versus time curve is
constructed and ∆T is determined.
Results
A.
Specific Heat of a Metal.
Procedure 1
and 2
Temperature of copper in beaker
|
82.0°C
|
Mass of calorimeter
|
3.10g
|
Mass of calorimeter + water
|
22.80g
|
Mass of water
|
19.70g
|
Table
1
Procedure 2
Time (s)
|
Temperature of water in calorimeter (°C)
|
0
|
31.0
|
60
|
30.0
|
120
|
30.0
|
180
|
30.0
|
240
|
30.0
|
300
|
30.0
|
Table
2
Procedure 3
Time (s)
|
Temperature of copper in calorimeter (°C)
|
0
|
30.0
|
30
|
30.5
|
60
|
30.5
|
90
|
30.5
|
120
|
30.5
|
150
|
31.0
|
180
|
31.0
|
Table
3
Graph 1
∆Twater
= Tfinal(water) – Tintial(water)
= (31.0 – 30.0) °C
= 1.0 °C
∆Tcopper
= Tfinal(copper) – Tintial(copper)
= (31.0
– 82.0) °C
= -
51.0 °C
Heat
lost by copper = - (Heat gained by water)
Specific
heat (copper) x mass (copper) x ∆Tcopper = - [Specific heat (water)
x mass (water) x ∆Twater]
s x 2.00g
x (- 51.0°C) = - (4.184 J g-1 °C-1 x 19.70g x
1.0°C)
s
= 0.808
Jg-1°C-1
The specific heat
for copper is 0.808 Jg-1°C-1.
B. Enthalpy (Heat) of Solution for the
Dissolution of a Salt
Mass
of calorimeter
|
2.47g
|
Mass
of calorimeter + water
|
21.60g
|
Mass
of water
|
19.13g
|
Table
4
Procedure 1
Time (s)
|
Temperature of water in calorimeter (°C)
|
0
|
|
15
|
30.0
|
30
|
30.0
|
45
|
30.0
|
60
|
30.0
|
Table
5
Procedure 3
Time (s)
|
Temperature of Na2S2O3
in calorimeter (°C)
|
0
|
24.0
|
15
|
24.5
|
30
|
24.0
|
45
|
23.5
|
60
|
23.0
|
75
|
23.0
|
90
|
23.0
|
105
|
23.0
|
120
|
23.0
|
135
|
22.0
|
150
|
22.0
|
165
|
22.0
|
180
|
22.0
|
Table 6
Graph 2
Based
on the graph,
∆Twater
= Tfinal(water) – Tintial(water)
= 22.0 °C – 24.0 °C
= - 2.0 °C
Gradient
of slope in the graph = (22-24)/(135 – 30)
= -0.019
Heat
lost by water = - (Heat absorbed for the dissolution of Na2S2O3)
Heat
lost by water, QH2O = Mass (water) x Specific heat (water) x ∆T
= 19.13 g x 4.184 J g-1 °C-1 x (- 0.019 °C)
= - 1.525 J
Heat absorbed for the dissolution of Na2S2O3
is 1.525 J.
The heat flowed from Na2S2O3
to the water.
Discussion
The water bath done on the copper was to
provide the copper an even and stable heating. It was boiled in a heater for
about 7 minutes, so that the heat of the copper and the water bath was
maintained in thermal equilibrium after a high enough temperature was reached,
the temperature of the copper is the same as the temperature of the water bath.
To obtain the temperature of water in stable conditions, the water was not used
in the calorimeter directly. Instead, it was left to reach thermal equilibrium
for 5 minutes, where the rate of heat gained from the surrounding eventually
reached the same rate as the heat loss to the surrounding. Even though the
copper was transferred into the calorimeter as quickly as possible, there was
still some heat loss to the surrounding. The calorimeter is made from
styrofoam, which has very low heat absorption, to minimize the heat of copper
to be absorbed by the calorimeter itself.
The temperature of the water rose when the
copper was added into it, because heat from the copper was transferred to the
water. Stirring was done gently and continuously so that the heat of the water
was even, thus temperature of the water taken would be more accurate. The graph
plotted was not a smooth line. The thermometer was not sensitive enough to
measure the slight rise of the water temperature. It has sensitivity up to 0.5
degree Celsius. Therefore, the temperature taken from the measurement had
distinct readings, from 30.0 to 30.5 to 31.0.
From this experiment, the specific heat of
copper was calculated to be 0.808 Jg-1°C-1. This showed a
significant difference from the actual specific heat of copper, which is 0.385
Jg-1°C-1. This might due to the inaccurate reading by the
thermometer. Besides, heat gained from the environment would also contribute to
a higher specific heat in calculation.
In Part B of the experiment, the water
temperature in the calorimeter dropped when Na2S2O3 was
added into it. This showed that there was a flow of heat from the water to the
salt, Na2S2O3. In the dissolution of salt, the
direction of heat flow is from the surrounding to the salt. Heat absorbed from
the surrounding or incomplete dissolution of the salt caused result of this
experiment to be lower than the supposed heat capacity of the salt.
1. What is the
difference between specific heat and heat capacity? What are the units for
these two quantities? Which is the intensive property and which is the
extensive property?
The specific heat is the amount of heat
required to change the temperature of one gram of a substance by one degree
Celsius or Kelvin. Specific heat is an intensive variable because it is
independent of the amount of substance present. It has a unit of Jg-1°C-1 or
Jg-1°K-1.
The heat capacity of a substance is the amount
of heat required to change its temperature by one degree Celsius or Kelvin,
where the mass of the substance is not considered. It has a unit of J°C-1.
The heat capacity is an extensive variable since a large quantity of matter
will have a proportionally higher heat capacity. In brief, the heat capacity is
dependent on the amount of substance present.
2. A 20.94 g sample of an unknown metal
is heated to 99.4oC in a hot water bath until thermal equilibrium is
reached. The metal is quickly
transferred to 100 ml of water at 22.0 oC contained in a Styrofoam
cup. The thermal equilibrium temperature
of the
metal plus water mixture is 24.6 oC. What is the specific heat of the metal?
Mass of water = Density (water) x volume
(water)
= 1 g/cm3 x 100cm3
= 100 g
Heat lost by metal = - (Heat gained by
water)
Specific heat (metal) x mass (metal) x ∆Tmetal
= - [Specific heat (water) x mass
(water) x ∆Twater ]
s x 20.94 x (24.6 – 99.4) = - [4.184 x
100 x (24.6 – 22.0)]
s = 0.6945 Jg-1°C-1
The specific heat
of the metal is 0.6945 Jg-1°C-1.
3. Magnesium metal reacts with
hydrochloride acid according to the following equation.
Mg (s) + 2HCl
(aq) à Mg Cl2 (aq) + H2
(g)
When 0.425 g of magnesium was added to 150.0ml of 1.00 M HCl in a
coffee-cup
calorimeter the temperature of the
solution increased from 24.5 oC to 35.3 oC. Given
that the heat capacity of the
calorimeter is 125 J/oC and that the density of the HCl
solution is 1.00 g/ml, calculate the
heat released per mole of magnesium.
Qsystem = Ccalorimeter x ∆T
= 125 JoC-1
x (35.3 – 24.5)oC
= 1350
J
Number of moles of Mg
= 
= 0.0177 mol
Heat released per mole of Mg = 
= 76235.29 J/mol
=
76.24 kJ/mol
Conclusion and Recommendations
Conclusion
Based on the
results of the experiment, the specific heat of copper is 0.808 Jg-1°C-1.
The heat capacity of Na2S2O3
is 1.525 J.
Recommendations
Two layers or more polyform cups could
be used to provide better heat insulation. Wind shield could be placed around
the set up of the experiment to minimize the air flow, which would increase the
rate of heat transfer to the surrounding through conduction, convection and
radiation.
A thermometer of greater sensitivity
could be used.
During the experiment, all fans should
be switched off to minimize air resistance.
References
·
Chang, Raymond (2003). General Chemistry.3rded. New York
·
Umland and Bellama (1999). General Chemistry. 3rd ed. Pacific Grove , CA
·
Zumdahl, Steven S (2005).
Chemical Principals. 5thed. New York
·
http://www.science.uwaterloo.ca/
·
http://www.chm.davidson.edu/chemistryAplets/calorimetry/specificHeatcapacityofcopper.html
http://sitinorfadhilah.says.com/recommendations/win-prizes-everydayMore detailed ^^
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